Phased array antennas are sometimes utilized in the searching and the tracking of aircraft from a fixed site. The antennas are physically large requiring a building to support an antenna face. In a typical installation wherein such an antenna is located on the shore of the ocean for monitoring the aircraft flying over the ocean, two or more antenna faces may be employed with the faces being angled to each other to provide adequate azimuthal coverage of the air space. The use of many radiating elements with their respective phase shifters in each face permits the formation of a highly directive radiation pattern as well as the deployment of greater power than that of smaller antennas. The transmitters for such antennas may well employ a number of power amplifiers, such as klystrons or traveling wave tubes (TWT), which are operated in parallel to provide greater power to a transmitted signal than that which can be provided by only one power amplifier.
A problem arises in that it is frequently desirable to be able to direct the power selectively to one or another of the faces, to evenly distribute the power among the faces, to permit the sequential operation of groups of the power amplifiers for producing a longer duration radiated signal pulse of increased energy but within the duty cycle of the phase shifters, and to connect the power amplifiers to the radiating elements in a configuration wherein the loss of the use of a single power amplifier does not noticeably degrade the radiation pattern. The foregoing requirements necessitate a form of switching, but the switching of high power, such as the high power of a TWT, is not readily accomplished in a situation which requires the switching of power rapidly from one aircraft target to another in a multiple target tracking situation.